In order to provide a higher data rate to mobile subscribers, the Advanced Lone Term Evolution system (Long Term Evolution Advance, “LTE-A” for short) proposes a carrier aggregation (“CA” for short) technology for the purpose of providing a wider bandwidth to User Equipments (“UE” for short) that have corresponding capability, and improving the peak rates for the UEs. In the LTE, the widest downlink transmission bandwidth supported by the system is 20 MHz. By carrier aggregation, two or more component carriers (“CC” for short) are aggregated to form a cell so as to enable the cell to support downlink transmission bandwidth wider than 20 MHz but not exceeding 100 MHz. A cell using the carrier aggregation technology is called a carrier-aggregation cell or a cell of carrier aggregation.
The component carriers in the cell of carrier aggregation can be divided into backward compatible component carriers and non-backward component carriers on the basis that whether they are compatible with the LTE. The non-backward component carrier only allows to be used by a UE supporting LTE-A technology. Not all of the component carriers need to broadcast system messages and paging messages, and not all of the component carriers have random access resources. When to access a carrier-aggregation cell, a UE can access the cell from any arbitrary chose component carrier having the random access resources. After the successful access, a base station can allocate other component carriers to the UE through dedicated signaling (e.g. Radio Resource Control (“RRC” for short) Connection Reconfiguration (RRC Connection Reconfiguration)) according to service requirements.
In a mobile communication system, in order to assure the service quality and provide good service experiences to users, after a UE in a certain cell establishes a connection with a network, the UE needs to measure the signal qualities of the serving cell and the neighboring cells to choose an appropriate cell to perform a handover, so as to satisfy the mobility requirement. Take the measurement within an LTE system in the LTE system as an example. The network instructs the UE to perform measurement by sending a measurement control message to the UE, wherein the measurement control message comprises: a measurement object (“MO” for short), the MO being a frequency of the LTE; a measurement report configuration (report configuration, “RC” for short), the RC configuring the attribute of a measurement report, for example, whether the measurement report being an event report or a periodical report, and corresponding configuration parameters; and a measurement ID (“MID” for short), the MID being an identity of each specific measurement task and associated with one MO and one RC so as to uniquely indicate one measurement task, i.e. uniquely indicating measurement configuration information on a certain frequency. In addition, the measurement control message further comprises a measurement threshold (s-Measure), which represents the signal quality threshold of a resident cell; a measurement quantity configuration (quantity configuration), which is configured to indicate a specific measurement quantity; and a measurement gap configuration, which is configured to perform inter-frequency and inter-RAT measurements during this measurement gap, etc. The UE can acquire the number of measurement tasks according to the number of the MIDs, and obtain the attributes of the measurement tasks according to the MOs and RCs corresponding to the MIDs, for instance, how to perform measurement and how to report.
The UE is required to measure the serving cell and the neighboring cells and report measurement objects that meet event triggered conditions, in order to satisfy the mobility requirement of the UE in a connected state, wherein measurement events for the serving cell mainly comprise: an A1 event, where the entry condition of the measurement event is that the signal quality of the serving cell exceeds a predetermined threshold; and an A2 event, where the entry condition of the measurement event is that the signal quality of the serving cell is lower than the predetermined threshold. And measurement events for the neighboring cells mainly comprise: an A3 event, where the entry condition of the measurement event is that the signal quality of a neighboring cell is higher than the signal quality of the serving cell by a predetermined offset; an A4 event, where the entry condition of the measurement event is that the signal quality of a neighboring cell exceeds a predetermined threshold; and an AS event, where the entry condition of the measurement event is that the signal quality of the serving cell is lower than a predetermined threshold 1 and the signal quality of the neighboring cell is higher than a predetermined threshold 2.
For the measurement of the above types of events satisfying the mobility requirement, the UE performs an event evaluation for the measurement result of each measurement object according to the measurement configuration parameters configured by the network, stores cells meeting the event entry conditions into a cell list corresponding to the measurement identity, and then acquires several cells (the number of reported cells should not exceed an upper threshold of the number of the reported cells as specified by the network) from the cell list corresponding to the measurement identity in an order according to signal qualities from strong to weak to generate a measurement report and to send the measurement report to the network.
As to the measurement of the measurement objects, different measurement quantities are measured in different systems. All of them reflect the signal quality or signal intensity of a cell. In the LTE, what is measured by the UE is Reference Signal Received Power (“RSRP” for short, unit of which is dBm) or Reference Signal Received Quality (“RSRQ” for short, unit of which is dB).
Each cell in a LTE system has only one frequency, thus it only needs to take a single frequency as the measurement object during the measurement. Correspondingly, during the event evaluation, it only needs to evaluate the signal quality of a cell on a single frequency (for example, A1, A2, A4 events) or evaluate the signal quality of neighboring cells with respect to a serving cell on a single frequency (for example, A3, A5 events); and it also only needs to take a cell on a single frequency as a processing object for measurement reporting and handover. However, as the carrier aggregation is introduced into the LTE-A, one cell using the carrier aggregation has a plurality of component carriers, then if the existing measurement mechanism in LTE is adopted, the measurement results on respective component carriers are reported independently, and the measurement results on respective component carriers received at the network are temporally discrete, i.e. the network cannot correctly and comprehensively evaluate the channel quality of the carrier-aggregation cell because the network can only acquire the measurement result on a single component carrier at one time point; thus when the UE performs handover between the cells of carrier aggregation, the service quality cannot be assured to satisfy good performance of user mobility between the carrier-aggregation cells.